The present invention relates to a semiconductor-device assembly method and a semiconductor-device assembly apparatus, in which an assembly method for simultaneously assembling a plurality of micro functional chips, i.e., semiconductor devices or the like, onto a mounting substrate is used.
Techniques for assembling micro functional chips, such as electronic components, onto a mounting substrate, such as a wafer or substrate, simultaneously in a single operation to fabricate semiconductor devices have been attracting considerable attention recently. At present, assembly process for mass production is normally being performed by pick and place technique in which assembly robots pick functional chips and place them in predetermined locations. However, since the cost and speed of the assembly robots are limited, it is necessary to find an alternative means which enables the assembly of a large number of functional chips with higher speed and lower cost.
As one of the technologies considered for this purpose, fluidic self assembly (FSA) has been proposed recently. The FSA technology is a technique for assembling in a fluid a plurality of functional chips onto a mounting substrate in a self-aligned manner.
Hereinafter, a conventional FSA process will be described with reference to FIGS. 7 and 8.
FIG. 7 schematically illustrates a semiconductor-device assembly apparatus 300A in which a FSA process according to a first conventional example is used. As shown in FIG. 7, a mounting substrate 410 is a wafer or a printed circuit board, has on its surface a plurality of recesses 410a for specifying assembling positions, and is held in a fluid with its surface inclined with respect to the surface of the fluid. Then, a fluid 311 in the form of slurry, in which a large number of functional chips 400 has been spread, is poured over the surface of the mounting substrate 410 through a pipette 310. The functional chips 400 are typically in the shape of a square, disc, or sphere. The numerous functional chips 400 contained in the fluid 311 poured over the surface of the mounting substrate 410 fit, by chance and naturally, into the empty recesses 410a having the matching shape, while sliding on the surface of the mounting substrate 410.
FIG. 8 schematically illustrates a semiconductor-device assembly apparatus 300B with a bubble pump according to a second conventional example. As shown in FIG. 8, the bubble-pump-equipped semiconductor-device assembly apparatus 300B is composed of a container 312, in which a fluid 311 and a mounting substrate 410 are placed, and a bubble pump system 313 for circulating functional chips 400.
The bubble pump system 313 carries the functional chips 400 that have not yet been disposed into recesses in the mounting substrate 410, to a position higher than the mounting substrate 410 by the buoyancy of bubbles 311a. The carried functional chips 400 are then poured over the surface of the mounting substrate 410 again. The bubbles 311a are created by a bubble-velocity controller 313a provided in the lower portion of the bubble pump system 313 from nitrogen gas 314 supplied to the bubble pump system 313.
However, in the conventional semiconductor-device assembly apparatus, the probability that the functional chips fit into the recesses in the mounting substrate depends upon the density of the recesses. Therefore, in order to achieve a high assembling efficiency, an enormous number of functional chips have to be prepared as compared with the density of the recesses. On the other hand, in the bubble pump shown in FIG. 8, the functional chips that have not been placed into the recesses can be reused, which allows the number of necessary functional chips to be reduced. Nevertheless, the assembling efficiency achievable by these types of semiconductor-device assembly apparatuses is limited and depends upon the shape of the semiconductor devices, for example. For instance, it has been reported that when disc-like functional chips having a given thickness and a given size were replaced with square-shaped functional chips, the assembling efficiency dropped from over 90% to less than 40%. This indicates that functional chips having a smaller number of symmetry axes have lower assembling efficiency. Therefore, it can be concluded that if square-shaped functional chips are replaced with rectangular functional chips, the assembling efficiency may be reduced to about half, as the square has four symmetric edges, while the rectangle has only two symmetric edges. If these rectangular functional chips are further made directional as required for semiconductor lasers, the assembling efficiency may be further reduced to half, and the assembling efficiency finally obtained may not exceed 10%. Since the assembling efficiency of functional chips is usually required to exceed 99% (at least 90%), there is a demand for a method which enables functional chips to be assembled with high assembling efficiency and accuracy, irrespective of the size and shape of the functional chips.